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There has been concern in recent years about the concentration of our seed heritage into the hands of a few large multinational corporations.

Very few of the food plants that our grandparents and great-grandparents sowed and ate still exist. The seeds they brought here, sowed and saved from year to year were gradually acclimatised to local growing conditions. These have largely disappeared.

As a response, various gardening groups have organised seed-saving and exchanges to preserve heritage seed varieties. However, such initiatives remain modest.

In garden centres you will find hundreds of varieties of vegetable and fruit seeds, mostly produced by large multinational seed companies. Home gardeners would seem to be spoilt for choice when they eye up the seed racks. However, on closer scrutiny, the choice is far more limited than we realise.

Most seeds sold in New Zealand have been grown overseas, so may be less suited to the New Zealand environment. Many seeds are F1 hybrids typically bred for high yields and commercial advantages such as appearance, transportability and long shelf life.

These seeds will produce one crop with a reasonable yield but subsequent generations of hybridised plants are wildly unpredictable. The gardener has to buy a new packet of seed the following year. This has meant most of the food we grow ourselves now lies in the hands of a few multinational companies.

The UN Food and Agricultural Organisation (FAO) have stated that 75 per cent of the world's food is generated from only 12 plants and five animal species. Out of 30,000 known edible plant species, three (rice, maize and wheat) provide almost 60 per cent of calories and proteins.

Three huge Big Ag mergers in 2016 are threatening to entrench a food system that reduces nature's edible abundance to a handful of plants on your plate.

If all these mergers succeed, three agrochemical companies -- Bayer with Monsanto, Dow with DuPont and ChinChem with Syngenta -- will sell over 60 per cent of the world's patented seeds. Many independent seed producers have been bought out or gone out of business in recent years.

The biggest of the deals is the one in which Monsanto, the world's largest seed company, has been purchased by Bayer, the German pharmaceutical and agrochemical multinational. Bayer -- which paid $90 billion -- will become the world's largest seed company with more than 25 per cent share of the global market in seeds.

These deals will likely leave gardeners paying more for seeds with less choice, and could accelerate the decline in the diversity of what we plant and eat.

The question now is whether US and EU regulators will intervene to prevent unprecedented control to be exercised by these mega-seed companies.

Margrethe Vestager, the European Commissioner for Competition, has submitted the mergers for review, saying farmers and consumers should have choices. She is under pressure from the EU Parliament.

In the US, it remains to be seen whether the Department of Justice will exercise its authority to stop the merger of Bayer and Monsanto. Both are lobbying "heavyweights" with an arsenal of lobbyists to make sure that government takes their side.

Former House Speaker Newt Gingrich is now lobbying hard on the Bayer team. President Trump appeared to favour the Bayer and Monsanto merger when he met recently with the two corporations' executives.

If all three mergers go through, it will lead to a frightening concentration of the seed industry. We can hope that in coming weeks US and EU regulators consider Monsanto plus Bayer and the other two mergers a "step too far".

These developments make it imperative that gardeners place greater emphasis on using open-sourced seed varieties which they save, swap and exchange.

Whanganui gardeners can swap surplus heirloom and open pollinated seeds at the Heritage Seed Swap Group that meets every year in August.

�David Hughes moved to Whanganui after working for 35 years in England, Australia, New Caledonia, France and other countries. He works as a translator from French into English and is involved in a project growing heritage wheat varieties.